Carrier sensing, which is a fundamental medium access protocol for IEEE 802.11 Distributed Coordination Function (DCF) devices, may function poorly when the RF environment at the transmitter and receiver are vastly different. For example, a terminal such as a transmitter begins sending a frame after determining a medium is free, but high interference and noise levels at the receiver may cause the frame to be received erroneously at the intended receiving terminal. Retransmission of the same data may degrade link throughput even further. The exchange of Request-To-Send (RTS) and Clear-To-Send (CTS) frames before sending of the data frames is intended to mitigate this problem. However, the sending of RTS and CTS frames for every data frame is inefficient particularly for wireless links, and even further over large distances, leading to long transmission latency.
Another problem with an IEEE 802.11 DCF based medium access protocol is that it requires terminal devices on both sides of a wireless link to operate on the same channel for transmissions and receptions since a Clear Channel Assessment (CCA) needs to be performed before any frame exchange sequences can be initiated. In a congested RF environment, there may be no single frequency band available for the wireless link. In addition, when the transmitter and receiver are separated by a long distance their respective local radio environments are likely to be significantly different, further reducing the likelihood of a single frequency band being optimal for both the forward and reverse wireless links.